Recovering hydrocarbons from subterranean zones typically involves drilling wellbores.
Wellbores are made using surface-located drilling equipment which drives a drill string that eventually extends from the surface equipment to the formation or subterranean zone of interest. The drill string can extend thousands of feet or meters below the surface. The terminal end of the drill string includes a drill bit for drilling (or extending) the wellbore. Drilling fluid, usually in the form of a drilling “mud”, is typically pumped through the drill string. The drilling fluid cools and lubricates the drill bit and also carries cuttings back to the surface.
Bottom hole assembly (BHA) is the name given to the equipment at the terminal end of a drill string. In addition to a drill bit, a BHA may comprise elements such as: apparatus for steering the direction of the drilling; sensors for measuring properties of the surrounding geological formations (e.g. sensors for use in well logging); sensors for measuring downhole conditions as drilling progresses; one or more systems for telemetry of data to the surface; stabilizers; heavy weight drill collars; pulsers; and the like. The BHA is typically advanced into the wellbore by a string of metallic tubulars (drill pipe).
Instead of driving a drill bit by rotating the entire drill string from the surface a drill bit may be driven by a mud motor. A mud motor is driven by the flow of drilling fluid through the drill string. Mud motors must work in harsh downhole environments. WO 2010/106335 describes a drill motor equipped with stabilizer blades that carry reaming blocks of diamond-impregnated tungsten carbide material along longitudinal edges of the blades.
As drilling progresses, especially where the formation being drilled is very hard, the drill bit can wear. The diameter of the wellbore being drilled may be reduced as the drill bit becomes worn. Reamer tools may be subsequently used to expand the wellbore to a required diameter. Reamer tools may be connected at various locations in the drill string. For example, U.S. Pat. No. 7,562,725 describes a reamer located between a mud motor and a drill bit.
Other references describing reamers of various types for downhole applications include: CA 2756010; US 2004/0099444; US 2006/0207796; US 2006/0237234; US 2010/0096189; US 2010/0326731; US 2011/0240370; US 2012/0279784; US 2013/0092444; U.S. Pat. No. 6,470,977; U.S. Pat. No. 6,848,518; U.S. Pat. No. 5,649,603; U.S. Pat. No. 4,480,704; WO 2010/151796; and, WO 2013/052554.
There remains a need for alternative tools and methods for subsurface drilling.